1. Field of the Invention
The present invention relates to a method of producing a semiconductor device and a configuration thereof. More particularly, it relates to a method of producing a resin-sealed semiconductor device and a configuration thereof which make it possible to decrease the size, thickness, weight and cost of the device.
2. Description of the Related Art
FIGS. 15A and 15B show a gull-wing type semiconductor device with the configuration of the prior art, FIG. 15A being a cross sectional view thereof and FIG. 15B being a top view thereof.
A semiconductor device of this configuration is generally produced in such steps as shown in FIG. 16, in a procedure described below. A semiconductor element 3 is bonded by means of a die bonding material 2 on an island 24 of a lead frame 6 which has the islands 24 and leads 1 as shown in FIG. 17. Then after connecting an inner lead section of the lead 1 surrounding the island 24 to an electrode pad located on the semiconductor element 3 by wire bonding using a wire 4 such as gold wire, the elements are sealed individually on both sides of the lead frame 6 by using a sealing resin 5. FIG. 18 is a top view of the semiconductor device with the configuration of the prior art after being sealed with resin. In a last stage, an outer lead section of the lead 1 is plated with tin or the like, cut off from the lead frame 6 and formed in gull wing shape, thereby to obtain the semiconductor device as shown in FIGS. 15A and 15B.
In the production method of the prior art, it is necessary to prepare the lead frame 6 having the islands 24 matched to the size of the semiconductor elements 3 and molding dies (not shown) for sealing the individual semiconductor elements with a resin. Therefore, when semiconductor elements 3 of different specifications are used, it is necessary to prepare different lead frames 6 and different molding dies for the various specifications.
In the semiconductor device of the prior art shown in FIGS. 15A and 15B, there has been a limitation on the reduction of the size and weight because the resin covers both sides of the lead frame 6.
Moreover, because heat generated by the semiconductor element 3 is dissipated through the lead 6, it is difficult to apply the device to high-output power transistors which generated much heat. Because of the relatively long connection between the semiconductor element 3 and a mother board, it is also difficult to apply the device to high-frequency transistors or the like.
To counter such problems as described above, a molded transistor having only one side of a lead being molded with a resin is disclosed, for example, in Japanese Patent Kokai Publication No. 62-134945. However, since production of such a molded transistor requires different lead frames for different specifications as in the prior art and molding with the resin is carried out individually for each semiconductor element, different molding dies must be prepared according to different specifications and therefore the above problems are not solved.
Also the devices are mounted on the mother board by using flat leads according to this prior art technology, but it cannot be applied to devices which generate much heat because of relatively small lead area.
An object of the present invention is to provide a method of producing the semiconductor device wherein semiconductor element are sealed with resin by using the same lead and independent of the specifications of the semiconductor elements, and a semiconductor device which can be reduced in size and weight and has good heat dissipation performance and high-frequency performance.
The present inventors have intensively studied. As a result, they found that semiconductor devices can be produced with a same lead frame regardless of the specifications of semiconductor elements when a plurality of the semiconductor elements are mounted on the lead frame having leads disposed substantially parallel to each other and, after sealing the whole with a resin, the individual semiconductor devices are cut off, and that the semiconductor device has improved heat dissipation performance and high-frequency performance. Thus, the present invention has been accomplished.
The present invention provides a method of producing a semiconductor device comprising a die bond pad, a wire bond pad, a semiconductor element mounted on the die bond pad, and a sealing resin for molding the semiconductor element, which comprises preparing a lead frame having a plurality of leads disposed substantially in parallel to each other at intervals in the longitudinal direction in the same plane; bonding a plurality of semiconductor elements in parallel on at least one lead surface of the lead frame; electrically connecting an electrode of each semiconductor element and another lead adjacent therewith in the longitudinal direction; molding the plurality of semiconductor elements together by means of the sealing resin applied from above the lead surface so that the back side of the lead is exposed; and cutting the lead and the sealing resin in the longitudinal direction between the semiconductor elements, thereby to take the lead with the semiconductor element being mounted thereon as a die bond pad, and to take the lead connected to the electrode of the semiconductor element as a wire bond pad.
With this method of producing the semiconductor element, because it is not necessary to prepare a plurality of lead frames for different sizes of the semiconductor elements to be mounted, the lead frame can be used in common, and therefore it becomes possible to simplify the production process and reduce the production cost.
Particularly with this method, since the semiconductor devices are made by cutting off the lead frame whereon the semiconductor elements are bonded consecutively, no part of the lead frame will be wasted, so that product yield per unit area of the lead frame is improved and the production cost can be reduced.
The present invention also provides a method of producing the semiconductor device, wherein the back surface of the lead is covered with a resin sheet thereby to mold with the sealing resin.
By providing such a step, the sealing resin is prevented from seeping through the space between the leads to the back surface of the lead during the sealing step, thus making it possible to prevent connection failure from occurring when connecting the semiconductor device to the mother board.
The resin sheet may be applied either to the entire back surface of the lead or to a part thereof.
Alternatively, the space between the leads may be filled with a masking material before applying the sealing resin.
Seeping of the sealing resin to the back of the leads can be prevented by filling the space between the leads with the masking material.
The present invention also provides a method of producing the semiconductor device, wherein the sealing resin which has seeped to the back surface of the lead is removed after applying the sealing resin.
By providing such a step, connection failure due to the sealing resin seeping to the back surface of the lead can be prevented.
The present invention also provides a method of producing the semiconductor device, wherein the leads are supplied in the form of a lead frame having electrically conductive leads fastened onto a frame substantially in parallel to each other at intervals in the same plane.
By using the lead frame having leads disposed parallel to each other, handling of the leads during the production process is made easier.
The size of the lead in the longitudinal direction whereon the semiconductor element is mounted is preferably equal to or less than the size of the semiconductor element in the longitudinal direction.
When the space between the leads is made equal to or less than the width of the semiconductor element, distance between the leads can be made larger even when the semiconductor device is made smaller, thus making it possible to prevent short circuit between the leads when connecting the semiconductor device to the mother board.
The semiconductor element may also be bonded on the lead surface by means of an electrically conductive or adhesive insulator.
When an electrically conductive resin is used, the semiconductor element and the die bond pad can be electrically connected.
The present invention also provides a method of producing the semiconductor device, wherein the sealing resin is cut off outside a plurality of semiconductor elements so that the plurality of semiconductor elements bonded on the different leads which are arranged in a direction perpendicular to the leads are molded in the same sealing resin.
By employing this method, it is made possible to easily produce the arrayed semiconductor device where the plurality of semiconductor elements are molded together in the sealing resin.
The present invention also provides a lead frame comprising a plurality of leads arranged substantially in parallel to each other in the longitudinal direction at intervals in the same plane.
The present invention also provides a semiconductor device comprising a die bond pad with a semiconductor element mounted on the top surface thereof; a wire bond pad arranged substantially in parallel to each other in the longitudinal direction while interposing the die bond pads therebetween; and a sealing resin for molding the semiconductor elements; wherein the sealing resin is applied from above the die bond pads and the wire bond pads so that the back surfaces of the die bond pads and the wire bond pads are exposed, while the space between the die bond pads and the wire bond pads is also filled with the sealing resin.
In a semiconductor device of such a configuration as described above, only the surface of the semiconductor device is sealed with the resin while the die bond pads and the wire bond pads formed by cutting off the leads are exposed on the back surface, and therefore it is made possible to connect the semiconductor device directly to the mother board by using the back surface of the semiconductor device, thus contributing to the reduction in the mounting area and height, size and weight of the device.
Also because the die bond pads and the wire bond pads are directly connected to the mother board, heat dissipation from the semiconductor element is improved so that the present invention can be applied to high output power elements, which generate much heat, as well.
Also because the distance of connecting the mother board and the semiconductor element can be reduced, good high-frequency characteristics can be obtained even when a high-frequency element is used for the semiconductor element.
Also bonding area for bonding the semiconductor device onto the mother board with solder or the like by using the die bond pads and the wire bond pads is increased, thus making it possible to increase the bonding strength.
The die bond pads and the wire bond pads are preferably provided to lie across both sides of the semiconductor device in the lateral direction of the semiconductor device.
By employing this configuration, areas of the die bond pads and the wire bond pads on back of the semiconductor device can be increased, thus making it possible to improve the heat dissipation and increase the bonding strength.
The space between the die bond pads and the wire bond pads may also be filled with a masking material instead of the sealing resin.
By using the masking material, it is made possible to prevent the sealing resin from seeping to the back of the leads.
The die bond pads and/or the wire bond pads preferably have a plurality of recesses on the top and/or the bottom surfaces.
By making recesses in the leads, contact area with the sealing resin applied thereon or with the solder used for connection to the mother board is increased, thus increasing the bonding strength and improving the reliability of the semiconductor device.
Also because the section area of the lead can be decreased with this configuration, cutting area during dicing is decreased leading to less load of cutting off and less wear experienced by the dicing blade.
The die bond pads and/or the wire bond pads preferably have a plurality of recesses provided on the side faces thereof.
This is because the contact area between the lead and the sealing resin can also be increased with this structure.
The recesses are preferably provided in such a way as the longitudinal cutting face of the die bond pad or the wire bond pad with the recess crosses either of the recesses.
The die bond pads and/or the wire bond pads preferably have longitudinal cross sections having trapezoidal shape with the top side greater than the bottom side.
Size of the die bond pad in the longitudinal direction is preferably equal to or less than the longitudinal size of the semiconductor element mounted on the die bond pad.
This is because a sufficient distance between the die bond pads and the wire bond pads can be maintained thus preventing the occurrence of solder bridge, even when the semiconductor device is made smaller thus reducing the distance between the die bond pads and the wire bond pads.
The present invention also provides a semiconductor device wherein the semiconductor element and other semiconductor element mounted on the other die bond pads arranged in a longitudinal array with the die bond pads, whereon the semiconductor elements are mounted, described above are molded together by means of the sealing resin.
This is because, by molding the plurality of semiconductor elements together as described above, the semiconductor device can be made smaller.
As will be clear from the above description, according to the method of producing the semiconductor element of the present invention, because it is not necessary to prepare lead frames suitable for the individual semiconductor elements to be mounted thereon and the lead frame can be used in common, the production process can be simplified and the production cost can be reduced.
Also because the lead frame with the semiconductor elements mounted thereon is sealed with the resin as a whole, it is not necessary to prepare different molding dies for various sizes of the semiconductor devices, thus the production process can be simplified and the production cost can be reduced.
Particularly because the lead frame with the semiconductor elements mounted thereon consecutively is cut off to make the semiconductor devices in the mass production, there is no part of the lead frame 6 wasted, so that product yield per unit area of the lead frame 6 is improved and the production cost can be reduced.
Also as the lead is provided with the recess, bonding strength with the sealing resin applied thereon or with the mother board can be increased thereby improving the reliability of the semiconductor device.
Also it is made possible to decrease the cut face area of the lead 1, reduce the load applied to the semiconductor device during cutting off and reduce the wear of the dicing blade.
Even when the distance between the die bond pad and the wire bond pad decreases as the size of the semiconductor device is made smaller, the distance therebetween can be maintained to a sufficient level, thereby preventing solder bridge from being formed.
Also in the semiconductor device of the present invention, only the front surface of the semiconductor device is sealed with the resin while the die bond pad and the wire bond pad formed on the back surface by cutting off the leads are exposed, the semiconductor device can be connected directly onto the mother board by using the back surface of the semiconductor device, thus making it possible to reduce the mounting area and height, thereby contributing to the reduction of size and weight.
Also because the die bond pad and the wire bond pad are connected directly to the mother board, heat dissipation from the semiconductor element can be improved, and the present invention can be applied to high-output power elements which generate much heat.
Also because the distance of connecting the mother board and the semiconductor element can be reduced, good high-frequency characteristics can be obtained when high-frequency element is used for the semiconductor element.
Also the bonding area for fastening the semiconductor device onto the mother board with solder or the like by using the die bond pads and the wire bond pads increases, thus making it possible to increase the bonding strength.